式起重机其实是桥式起重机的一种变形，主要是将它应用在室外的货场、料场货、散货的装卸作业方面。它的金属结构像门形框架，因此而得名，门式起重机。由于机械设备在承载主梁下安装两条支脚，所以可以直接在地面的轨道上行走。根据不同行业上使用的要求，门式起重机有细分为一下几种。
Crane is a kind of deformation of bridge crane, is mainly applied in the outdoor yard, loading and unloading cargo, bulk cargo market. Metal structure it like a door frame, hence the name, gantry crane. Due to mechanical equipment installation two feet on the bearing beam, so it can be directly in the ground track walk. According to the requirements of different industries, gantry crane is subdivided into several.
对于集装箱运输也来说，集装箱龙门起重机就比较合适，这种起重机的拖挂车可以将岸壁集装箱运载桥从船上卸下的集装箱运到堆场或后方后，通过集装箱龙门起重机堆码起来或直接装车运走。不仅加快了集装箱的周转速度，而且对其它起重设备也是有利的。
For transportation, container crane of Longmen more appropriate, trailer this crane can bridge to quay container carrying containers unloaded from the ship to the yard or rear, the container crane of Longmen stacking up or direct loading. Not only speed up the container turnover rate, but also beneficial to other hoisting equipment.
我们平时用的最多的一种是普通龙门起重机 ，因为这种起重机可以搬运各种成件物品和散状物料，只要起重量不超过一百吨，跨度四到三十五米之间的作业都可以，应用范围非常广、适应面也很强。用抓斗的普通电动单梁起重机工作级别较高。
We usually use most is an ordinary Longmen crane, because this kind of crane can carry a variety of items and bulk materials, as long as the weight of not more than one hundred tons, the span of four to thirty-five meters between the activity can be, very wide range of applications, the adaptation surface is also very strong. With the level of ordinary electric single girder crane high grab.
像在一些水电站，我们进行吊运、启闭闸门或安装作业用的都是水电站龙门起重机。这种起重机比较有针对性，起重量在八十到五百吨之间，跨度在八到十六米之间，是属于比较小的了。对于造船业来说，造船龙门起重机就再适合不过了。主要是用来进行船台拼装船体，一般有两台起重小车，一台有两个主钩，在桥架上翼缘的轨道上运行；另一台有一个主钩和一个副钩，在桥架下翼缘的轨道上运行，以便翻转和吊装大型的船体分段。
Like in some hydropower station, we are lifting, gate or installation work are used in Longmen crane hydropower station. This kind of crane more targeted, the weight between eighty to five hundred tons, the span in eight to sixteen meters, is relatively small. The shipbuilding industry, shipbuilding crane Longmen is suits. Is mainly used for ship hull general assembly, two sets of lifting trolley, one of two main hook, running on a bridge on the flange orbit; another has a main hook and an auxiliary hook, on the bridge under the flange orbit, to turn and lifting large hull section.